The pedal-start E50 is a very popular engine to modify for several reasons.

the wide availability of aftermarket and performance parts

its reputation as a reliable, durable, and fairly uncomplicated base for restoration or modification

the single speed and centrifugal clutch are very simple and not prone to failure at extremely high RPMs -- the power added by a kit is less likely to cause problems on an E50 than on a more complicated and difficult to rebuild two speedZA50 engine.

Top End

Cylinders

Many stock cylinders were manufactured for the E50 (and the ZA50 as well, as stock cylinders are compatible with both engines). Click here to see a page from the Puch manual explaining the differences between the stock Puch top ends (aluminum series 1-5 and high torque series 11-33).

Aluminum SeriesMain article: Puch cylinders (aluminum series)
There were the aluminum series cylinders, which have completely open transfer ports and are completely aluminum, with the exception of a plated bore. These cylinders are typically stamped with single digit designations like 1, 2, 3, etc. Some of these cylinders also came with very large intake ports where they connect to the intake manifold. However, the stock Puch intake manifolds and carburetors only came in 12mm and 14mm sizes, which do not take advantage of this large intake port.

An aluminum series cylinder

High Torque SeriesMain article: Puch cylinders (high torque series)
The other series typically found on E50s is the "hi-torque" or cast-iron series of cylinders. These cylinders are distinguishable from the aluminum series, because instead of having a plated cylinder bore, the bore is a part of a cast-iron cylinder sleeve which is surrounded by the aluminum cooling block/fins. Additionally, these cylinders were often painted black from the factory, but the paint had a tendency to peel off with time. These cylinders had closed transfer ports, and were given stamped double digit number designations, like 11, 22, 33, etc.

Naked cast-iron bore

Magnum Series
The last series of stock cylinders manufactured for the E50 and ZA50 was the Magnum series. These cylinders have physically larger outer dimensions, but they retain the same 49cc displacement as the other stock Puch cylinders. Like the "hi-torque" series, they had cast-iron cylinder sleeves. They also featured an angled exhaust port, which is different than the flat exhaust ports on the aluminum and cast-iron series.

Korado
In the 1990's, Puch (then owned by Piaggio) manufactured the Korado. The cylinder that came on this moped is aluminum, has a good squish band, came with large bridged transfers and a boost port, a single dykes ring piston, and an angled exhaust port. This cylinder/top end is highly sought-after by many performance tuners, because even without modification, it can perform better than some kits.

Cylinder Heads

Two styles of stock cylinder heads can be found on the E50 and ZA50 engines. There is a standard cylinder head, which has a large squish band and can be milled down for higher compression. There is also a "high compression" cylinder head which is slightly lower than the standard cylinder head, and thus raises compression.

Pistons

Stock pistons are still a realm of debate. Typically, all of the Puch cylinders ran a two-ring piston with thick piston rings. However, some have found other types of pistons in stock Puch cylinders. One variation is a single-ring piston, with the ring located much closer to the piston crown than on the standard two-ring Puch piston. Another variation is a two-ring piston with a dykes ring, or L-profile piston ring with the dykes ring closer to the crown. It has not yet been determined whether these came from the factory, or were aftermarket or repair parts added after the production of the moped. As such, the debate continues as to whether these were in fact stock pistons or not.

Bottom End

E50 oiling hole

The E50 bottom end remained mostly unchanged throughout the course of its production, with a few notable exceptions. The E50 bottom end is composed of 5 main parts: the engine cases, the crank, the clutch assembly, the flywheel/stator plate assembly, and the final drive gear.

IMPORTANT NOTE
There is a hole in the engine cases on the e50 engine. It is located in the right transfer ramp (as you face the engine case). That hole goes back to a bearing in which the crank sits. This hole allows oil to travel back to that bearing and lubricate it. Without that hole, the bearing will not receive lubrication, and is more likely to fail. Though it may look rough, the hole is meant to be there, and should not be filled. Rather, when putting on a performance cylinder kit, some people actually make the hole larger to allow increased lubrication to the crankshaft, since kits often bring the engine up to a higher RPM where more lubrication is desirable.

The typical setup found on the bottom end of an E50 is a crankshaft with a brass bushing in the small end of the connecting rod, a 2 shoe centrifugal clutch, and a 6 volt electrical system consisting of a flywheel and stator plate assembly. This model can only be started by pedaling, or by removing the clutch cover, and turning the flywheel with a drill.

Later E50 engines, mainly those found on the Puch Korado moped, had crankshafts which contained needle bearings in the small end of the connecting rods, 3 shoe centrifugal clutches, and 12 volt electrical systems with CDI ignitions. These engines also could be started with a kickstart assembly instead of the traditional pedal start.

How It Works

Starting

In the starting of a typical E50 (non-kickstart version), the clutch engagement lever is pulled on the handlebars, which forces the clutch to engage. Then, the moped is pedaled. This rotates the rear wheel, to which the rear drive sprocket is attached. The rear drive sprocket is linked to the front drive sprocket by a chain, and as the rear drive sprocket rotates, it forces the front sprocket to rotate as well. The front sprocket is located on the shaft of the final drive gear, and as the front sprocket turns, it forces the final drive gear to turn. The teeth of the final drive gear mesh with the teeth of the clutch assembly, and force it to turn. Due to the engagement of the clutch, all of this rotation is eventually transferred to the crankshaft, which starts the moped. In the auto-engaging version of the E50, there is no lever, but a starter clutch which grabs the clutch bell when the crank rotates.

Running

When the E50 is running, it functions thusly:
An intake charge is sucked into the cylinder through the carburetor, intake manifold, and intake port, filling the cylinder with a fresh charge of fuel/air mixture, which forces the burned exhaust gases out the exhaust port. The piston reaches bottom dead center, and begins moving upward in the cylinder once more. It closes off the intake and transfer ports, and compresses the fresh charge of fuel-air mixture in the cylinder head. The rotation of the crankshaft generates electricity via the magneto, which travels to the spark plug and causes a spark in the cylinder. The burning mixture expands rapidly, pushing the piston back down after it has reached top dead center. As the piston travels downward, it first opens the exhaust port, which allows some of the burning mixture to escape. As the piston is traveling downward, it also forces fresh mixture from the crankcase through the transfer ports. As the transfer ports are uncovered, they shoot fresh charge into the cylinder, along with the intake port, which opens shortly after them. The function of the transfer ports is to shoot fresh mixture into the cylinder in a looping pattern that 'sweeps' the remaining burned mixture out of the exhaust port without loosing too much of the fresh charge out the exhaust port as well. This fresh charge is taken in, and the cycle repeats.

The rotation generated by the crankshaft turns the clutch assembly. At a certain RPM, the clutch engages, and begins to rotate, transferring motion to the final drive gear, on which the front drive sprocket is located. The rotation of the front drive sprocket forces the rear drive sprocket to rotate. The rear drive sprocket is bolted to the rear wheel, and as it rotates, the rear wheel also rotates, moving the moped forward.

See Also

Performance Modifications

A wide range of performance parts are available for the E50 engine, including cylinder kits, larger carburetors, expansion chamber exhaust pipes, performance cranks, CDI ignitions, and 3 shoe clutches. There are two excellent articles on Puch cylinders: Puch Maxi Cylinder Information, which reviews different Puch cylinders, and Puch Cylinders, which contains a chart of different cylinders and speeds reached with those cylinders. You can also read reviews of the different exhausts available for Puchs in the article Puch Exhausts. All of these 3 articles were translated for us by SchijnHeilig. There is also an article for Puch E50 Crankshafts.